Primary-1yr to Rental-3yr and Back to Primary-1yr taxable gain?

[Yu Xiao]

Have a tax related question about capital gain tax exclusion for primary residence (which was converted to rental in 3 years). 

Year 1: Primary Residence

Year 2-4: Rental

year 5: Primary Residence

In this situation, I do meet the eligibility test (ownership and use) so qualify for the exclusion. But the trick comes with when i have to calculate taxable gain. Do I need to pro-rate non-use when reporting taxable gain?

From the IRS, "Determine your non-qualified use gain. Complete this section only if there is a period, after the year 2008, when neither you nor your spouse (or your former spouse) used the property as a main home, and that period of non-use occurred during the 5-year period prior to the date of sale and before the time when you or your spouse (or your former spouse) used the property as a main home"

1. If first 2 is primary, the later 3 if rental, then no pro-rate is needed. 

2. If first 3 rental, the last 2 year primary. Then I need to prorate for non-use. Which means I only get 2/5 * 250K =100k capital gain tax free. 

But what about my situation that my rental period is in between my primary residence use? 

Does anyone know? 

Thanks!